1. Field of the Invention
The invention relates to a method for detecting a potentially destructive state of an-arrangement containing electronics and for terminating this state, whereby currents I1, I2, . . . , In, consumed by the electronics, via connecting means from at least one supply voltage, are continuously compared with memorized maximum permissible currents Im1, Im2, . . . , Imn, and whereby the connecting means are disconnected from the at least one supply voltage and are subsequently earthed as soon as at least one consumed current Ij is higher than the corresponding maximum permissible current Imj, with jxcex5{1,2, . . . , m}.
The method is aimed at preventing the breakdown of the electronics which particularly occurs as a result of a latch-up condition known in the art. The occurrence of latch-up causes at least one component contained in the electronics to be reduced to a state, not envisaged in the design or at least not considered possible, where the breakdown of this at least one component is inevitable, which will usually have an adverse effect on the system""s operational effectiveness. Latch-up may occur as a result of strong electromagnetic fields, static discharges, highly fluctuating supply voltages or high-energy particles.
2. Discussion of the Background
For professional equipment, designed for e.g. space or military applications, use is preferably made of components which are insusceptible to latch up. However, owing to their prohibitive prices, these components are unsuitable for use in less sophisticated equipment. Particularly for computer equipment, components of the four-layer type, highly susceptible to latch-up, are nearly always used.
Computer equipment has increasing popular appeal and has reached an exceptionally high state of perfection. Consequently, the use of COTS (Commercial-Off-The-Shelf) components even in professional applications is inevitable. There is a risk, however, that professional equipment becomes faulty as a result of latch-up of a component contained in COTS equipment. In space applications, this may occur as a result of solar activity coupled with high radiation levels. Equipment for military applications has to be immune to comparatively nearby nuclear explosions. In less sophisticated applications, latch-up may occur as a result of lightning striking in the proximity of the equipment or by problems encountered with, for instance, a ship or aircraft power supply system.
Thus, it is an object of the present invention to protect COTS equipment against the effects of latch-up, without modifying this COTS equipment as such.
The invention also relates to a protection system for detecting a potentially destructive state of an arrangement containing electronics and for terminating this state, provided with measuring means for measuring currents consumed in the operating mode by the electronics from at least one supply voltage, memory means for storing the maximum currents permitted by the electronics, a digital processor for continuously comparing consumed currents with corresponding, memorized currents and processor-controlled switching means for disconnecting the electronics from the at least one supply voltage and for subsequently connecting said electronics to earth if at least one consumed current exceeds the corresponding maximum permissible current level stored in the memory means.
For an arrangement to be protected different operating modes can be distinguished. Thus, the arrangement may be in the standby mode or may be fully operational. A favourable realization of the method is characterized in that for each operating mode, a set of maximum permissible currents valid for that particular operating mode is stored in memory.
Measurements show that the currents in the different operating modes generally depend on the ambient temperature in which the arrangement operates. An embodiment according to a further aspect of the invention which also takes account of a fluctuating ambient temperature is characterized in that for a number of ambient temperatures in each operating mode, a set of maximum permissible currents, valid for that particular temperature in that particular operating mode is stored in memory. It is then possible to derive for a particular ambient temperature a maximum permissible current from the maximum permissible currents stored for the most approximate temperatures, for instance on the basis of linear interpolation.
In changing over from a first mode to a second mode, certain currents may fluctuate in a time-dependent manner. More precisely, the current will, when activating a certain function, initially reach a peak level, for instance caused by the spin up of a motor or stepping of a stepping motor. A favourable realization of the method is thereto characterized in that these currents are stored in a time-dependent manner in the set of memorized maximum permissible currents.
The sets of maximum permissible currents are preferably determined for each separate device, since the statistical spread in the current consumption of electronic components, and consequently the spread in the current consumption of each separate device, may be considerable. A favourable method according to a further aspect of the invention which realizes this in a simple manner, is characterized in that in a preoperational phase, the consumed currents I1, I2, . . . , In are determined for the different ambient temperatures and operating modes and that the maximum permissible values Im1, Im2, . . . , Imn are derived from the values I1, I2, . . . , In, by multiplying these values by a factor. In a favourable realization, the factor is selected in the 1.05-1.2 interval.
In a favourable embodiment according to a further aspect of the invention, the protection system is characterized in that the arrangement distinguishes a number of different operating modes, that the memory means are designed to store, in each operating mode, a set of maximum permissible currents for a number of temperature ranges and that the processor is designed to compare, for each operating mode and each temperature range, the consumed currents with the corresponding set of maximum permissible currents.
A favourable embodiment according to a further aspect of the invention in which the sets of maximum permissible currents are obtained semi-automatically, is characterized in that the processor is also designed to determine, in a preoperational phase, the currents consumed per operating mode and per temperature range, these processor computations serving to determine the maximum permissible currents, and to store these maximum permissible currents in the memory means.